ortools-clone/examples/dotnet/tsp.cs

// Copyright 2018 Google
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

using System;
using System.Collections.Generic;
using Google.OrTools.ConstraintSolver;

/// <summary>
///   This is a sample using the routing library .Net wrapper to solve a TSP problem.
///   A description of the problem can be found here:
///   http://en.wikipedia.org/wiki/Travelling_salesman_problem.
/// </summary>
public class TSP {
  class DataProblem {
    private int[,] locations_;

    // Constructor:
    public DataProblem() {
      locations_ = new int[,] {
        {4, 4},
          {2, 0}, {8, 0},
          {0, 1}, {1, 1},
          {5, 2}, {7, 2},
          {3, 3}, {6, 3},
          {5, 5}, {8, 5},
          {1, 6}, {2, 6},
          {3, 7}, {6, 7},
          {0, 8}, {7, 8}
      };

      // Compute locations in meters using the block dimension defined as follow
      // Manhattan average block: 750ft x 264ft -> 228m x 80m
      // here we use: 114m x 80m city block
      // src: https://nyti.ms/2GDoRIe "NY Times: Know Your distance"
      int[] cityBlock = {228/2, 80};
      for (int i=0; i < locations_.GetLength(0); i++) {
        locations_[i, 0] = locations_[i, 0] * cityBlock[0];
        locations_[i, 1] = locations_[i, 1] * cityBlock[1];
      }
    }

    public int GetVehicleNumber() { return 1;}
    public ref readonly int[,] GetLocations() { return ref locations_;}
    public int GetLocationNumber() { return locations_.GetLength(0);}
    public int GetDepot() { return 0;}
  };


  /// <summary>
  ///   Manhattan distance implemented as a callback. It uses an array of
  ///   positions and computes the Manhattan distance between the two
  ///   positions of two different indices.
  /// </summary>
  class ManhattanDistance : NodeEvaluator2 {
    private int[,] distances_;

    public ManhattanDistance(in DataProblem data) {
      // precompute distance between location to have distance callback in O(1)
      distances_ = new int[data.GetLocationNumber(), data.GetLocationNumber()];
      for (int fromNode = 0; fromNode < data.GetLocationNumber(); fromNode++) {
        for (int toNode = 0; toNode < data.GetLocationNumber(); toNode++) {
          if (fromNode == toNode)
            distances_[fromNode, toNode] = 0;
          else
            distances_[fromNode, toNode] =
              Math.Abs(data.GetLocations()[toNode, 0] - data.GetLocations()[fromNode, 0]) +
              Math.Abs(data.GetLocations()[toNode, 1] - data.GetLocations()[fromNode, 1]);
        }
      }
    }

    /// <summary>
    ///   Returns the manhattan distance between the two nodes
    /// </summary>
    public override long Run(int FromNode, int ToNode) {
      return distances_[FromNode, ToNode];
    }
  };

  /// <summary>
  ///   Print the solution
  /// </summary>
  static void PrintSolution(
      in DataProblem data,
      in RoutingModel routing,
      in Assignment solution) {
    Console.WriteLine("Objective: {0}", solution.ObjectiveValue());
    // Inspect solution.
    var index = routing.Start(0);
    Console.WriteLine("Route for Vehicle 0:");
    long distance = 0;
    while (routing.IsEnd(index) == false) {
      Console.Write("{0} -> ", routing.IndexToNode(index));
      var previousIndex = index;
      index = solution.Value(routing.NextVar(index));
      distance += routing.GetArcCostForVehicle(previousIndex, index, 0);
    }
    Console.WriteLine("{0}", routing.IndexToNode(index));
    Console.WriteLine("Distance of the route: {0}m", distance);
  }

  /// <summary>
  ///   Solves the current routing problem.
  /// </summary>
  static void Solve() {
    // Instantiate the data problem.
    DataProblem data = new DataProblem();

    // Create Routing Model
    RoutingModel routing = new RoutingModel(
        data.GetLocationNumber(),
        data.GetVehicleNumber(),
        data.GetDepot());

    // Define weight of each edge
    NodeEvaluator2 distanceEvaluator = new ManhattanDistance(data);
    //protect callbacks from the GC
    GC.KeepAlive(distanceEvaluator);
    routing.SetArcCostEvaluatorOfAllVehicles(distanceEvaluator);

    // Setting first solution heuristic (cheapest addition).
    RoutingSearchParameters searchParameters = RoutingModel.DefaultSearchParameters();
    searchParameters.FirstSolutionStrategy = FirstSolutionStrategy.Types.Value.PathCheapestArc;

    Assignment solution = routing.SolveWithParameters(searchParameters);
    PrintSolution(data, routing, solution);
  }

  public static void Main(String[] args) {
    Solve();
  }
}